CODEWITHSUNDEEP
c
user644814
user644814

Reputation: 13

how to understand "return *test== ‘\0’;"

There is a code snippet,

int matchhere(char *regexp, char  *text)
 {
    /* do sth */
    return    *test== '\0';
 }

I do not understand what does 

return    *test== '\0';

mean. Or what it will return? How does "==" function here?

Upvotes: 0

Views: 186

Answers (8)

John Bode
John Bode

Reputation: 123548

The statement

return *text == '\0';

is equivalent to 

return text[0] == '\0';

which is also equivalent to 

return text[0] == 0;

In each case, it's comparing the first character of the string pointed to by text to 0, which is the string terminator, and returning the result of the comparison. It's equivalent to writing

if (*text == '\0') // or *text == 0, or text[0] == 0, or !*text, or !text[0]
  return 1;
else
  return 0;

Another equivalent would be

return !*text; // or !text[0]

which will return 0 if *text is non-zero, 1 otherwise, but that's pushing the bounds of good taste.

Upvotes: 0

mouviciel
mouviciel

Reputation: 67859

*test represents the first character of a string.

== is the equality operator.

'\0' is the null character, which in C represents the end of a string.

*test== ‘\0’ is a logical expression which returns true whenever the string is empty.

The whole instruction returns that logical result to the caller.

Upvotes: 0

Hernán Eche
Hernán Eche

Reputation: 6898

It checks if *test is an empty string, in that case return a different from zero value

Upvotes: 0

GrahamS
GrahamS

Reputation: 10350

*test means the contents of the test pointer, which is a char.

*test == '\0' just compares that character to the null character.

return *test == '\0' means return the result of that comparison.

So basically, if test points to a null-character then matchhere() will return true, otherwise false.

Upvotes: 0

grysik44
grysik44

Reputation: 233

It checks if the character pointed by text pointer equals '\0' character (string-terminating character).

Upvotes: 0

DarkDust
DarkDust

Reputation: 92384

The *test part reads the first character for the C string (a C string is merely a bunch of characters starting at a given address, and the *foo operator looks at that address which happens to contain the first character). By definition, a C string ends with a null byte ('\0' or simply 0).

So this tests whether the first character is the end-of-string character. Or in other words: it tests whether the string is empty. That comparison result (1 if empty, 0 if non-empty) is returned.

Upvotes: 2

Lightness Races in Orbit
Lightness Races in Orbit

Reputation: 385264

It fails to compile because "test" is not the same as "text", and because there is no such type Int in C.

If the typos were fixed, it'd see whether the first letter of the buffer pointed to by text is the NULL character -- i.e. it returns 1 if the buffer is empty, and 0 otherwise.

Upvotes: 1

Erik
Erik

Reputation: 91300

compare *test to '\0', return 0 if inequal, return 1 if equal.

Upvotes: 3

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